Heart pump synchronizing apparatus



July 1, 1969 H. R. GuARlNd HEART PUMP SYNCHRONIZING APPARATUS /l ofzSheet Filed Aug. l5, 1966 `uly 1, 1969 H. R. GuARlNo l 3,452,739y

HEART PUMP SYNCHRONIZING APPARATUS Filed Aug. 15,l 1966 i sheet 3 nf 2"ADVANCE" MULTI- VIBRATOR HENRY R. GUARINO INVENTOR.

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ATTORNEYS United States Patent O 3,452,739 HEART PUMP SYNCHRONIZINGAPPARATUS Henry R. Guarino, Revere, Mass., assignor to Avco Corporation,Cincinnati, Ohio, a corporation of Delaware Filed Aug. 15, 1966, Ser.No. 572,472 Int. Cl. A61m 1/03 U.S. Cl. 128-1 8 Claims ABSTRACT OF THEDISCLOSURE A synchronizing circuit for circulatory assist systems thatfollows the patients heart beat. The patients R-wave is used to actuatea saw tooth generator which charges a capacitor which is also partiallydischarged by signals derived from the R-wave. The output signal of thesaw tooth generator Iand the voltage across the capacitor are comparedto provide a second signal prior to the arrival of the next succeedingR-Wave. This second signal trips a one shot multivibrator which in turntrips a second one shot multivibrator stable in one direction for aselectable time interval whereby the diastolic phase of the bloodpumping unit is adjustably caused to effectively begin with the systolicphase of the patients heart and terminate at a selectable subsequenttime interval.

This invention relates to heart pump apparatus and more particularly toapparatus for synchronizing circulatory assist systems wherein a bloodpumping unit is synchronized with the demands of a patients heart.

The `advent of open heart surgery has presented to the medicalprofession the opportunity of repairing damaged or diseased hearts ofindividuals and where appropriate, using circulatory assist systems inindividuals who without such correction and/or systems face prematuredeath. Many devices are involved in this type of surgery. For example,one circulatory assist system may comprise a valveless blood pumpconnected across the arch of the aorta and driven by fluid pressure inresponse to electronic signals (QRS wave) provided by the heart itself.By operating the blood pumping unit in proper phase, the systolicpressure in the left -ventricle can be reduced and the systemiccirculation can be maintained with a substantially reduced work load onthe heart muscle. In addition, the operation of the blood pumping unithas the eiect of shifting the phase of the normal systolic pressure sothat this pressure appears in the aorta at a time when the leftventricle is relaxed. Assuming competence of the normal aortic valve,one then has an increased perfusion pressure available to the coronaryarteries. It is believed that such an increase in coronary perfusion,together with a reduction in the effort required from the heart, shouldbe effective in a number of cases of cardiac insufficiency.

As may be seen from the above, the blood pumping unit must be capable ofbeing synchronized with the patients heart and, accordingly, animportant component of circulatory assist systems is electricallyoperated synchronizing or control means for synchronizing or controllingoperation of the blood pumping unit.

By using heart pump equipment for extended periods of time, it iscontemplated that the equipment may be utilized for regional perfusionsin therapeutic treatment of the heart. Still other use of the equipmentwill be to provide circulation of blood through an artificial organ suchas an external artificial kidney. In connection with this function ofthe apparatus, it should be noted that many research institutions atthis time are concentrating their research activities on providingartificial counterparts of other organs and whenever such applicationrequires circulation, the present invention may be utilized.

Implantable prior art pulsatile pumps usually consist of a flexible bulbor ventricle squeezed by pressurized fluids from a pumping or actuatingunit and is coupled to one or more blood vessels such as arteries orveins. Generally, arterial graft sections connect the bulb to thecirculatory system. These arterial graft sections are generally of thewoven Teflon type or Dacron type employed in the insertion of arterialgrafts and the replacement of damaged sections of an artery. EdwardsSeamless Arterial Graft manufactured by the United States Catheter andInstrument Company have been found to be satisfactory.

In most, if not all, circulatory assist systems, it is necessary asnoted above that the flexible bulb be synchronized with the patientsheart. A typical pneumatically driven and electrically controlledcirculatory assist system is broadly disclosed in U.S. Patent No.3,099,260. Other systems are disclosed in patent application No. 355,273iiled Mar. 27, 1964, and patent application No. 531,281 led Mar. 2,1966, to which reference is made and which are assigned to the sameassignee as this application.

In the use of circulatory assist systems, which, for eX- ample, utilizea valveless blood pumping unit, it is necessary that during its systolicstroke the heart ll the blood pumping unit and that accordingly, thelling or diastolic stroke of the pumping unit be actuated in phase withthe systolic stroke of the patients heart.

In accordance with the preferred embodiment of the invention, signalsderived from the R-wave actuate a linear saw tooth generator thatprovides a linearly increasing voltage which charges a storage capacitorwhich in turn is partially discharged by the said signals derived fromthe R-wave. The saw tooth voltage and voltage across the storagecapacitor are compared in a comparator to provide a second signal at aselectable time interval prior to the arrival of the next succeedingR-wave, and the second signal trips a one shot multivibrator which inturn trips a second one shot multivibrator stable in one direction for aselectable time interval whereby the diastolic phase of the bloodpumping unit is adjustably caused to effectively begin with the systolicphase of the patients heart and terminate at a selectable subsequenttime interval. Accordingly, an object of the present invention is theprovision of means for synchronizing a blood pumping unit with apatients heart.

Another object is the provision in a circulatory lassist system of asynchronizing circuit that is actuated by the R-Wave from a patientsheart.

A further object is the provision in a circulatory assist `system of asynchronizing circuit which follows the heart beat of `a patient.

A still further object is the provision in a circulatory assist systemfor controlling the operation of a blood pumping unit of a synchronizingcircuit which provides an output signal phased with the R-wave of thepatients heart and determined by the time interval between previousR-waves.

A still further object is the provision in a circulatory assist systemof a synchronizing circuit for providing output pulses which followchanges in a patients heart beat and which have an adjustable timeinterval with respect to a succeeding R-wave.

The novel features that are considered characteristic of the presentinvention are set forth in the appended claims; the invention itself,however, both as to its organization and method of operation togetherwith additional objects and advantages thereof, will best be understoodfrom the description of a specific embodiment when read in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a block diagram of a typical circulatory assist system;

FIGURE 2 is a block diagram of electrical components in accordance withthe invention comprising the synchronizing circuit of FIGURE 1; IandFIGURE 3 is a schematic diagram showing details of electrical componentsshown in FIGURE 2.

Directing attention now to FIGURE 1, there is shown a schematicillustration of a typical heart pumping or circulatory assist apparatusintended to provide 'intercorporeal mechanical assistance. As shown inFIGURE l, in a typical system a suitable pressurized source of gas 11feeds into a lo-W pressure regulator 12. lLarge oxygen bottles whicharea readily available and are a satisfactory source of oxygen aregenerally pressurized to a pressure of several thousand pounds andgenerally have a pressure regulator which, while not particularlysensitive, is satisfactory to provide a reduction in pressureapproaching that required for the actuation of the blood pumping unit. Asatisfactory pressure for the pumping unit has been found to beapproximately 3 pounds per square inch; hence, pressure regulator 12,while of conventional design, should permit small adjustments in thepressure range of about to 3 pounds per square inch. The output of thelow pressure regulator 12 is fed to a threeway solenoid actuated valve13. The valve 13, which is normally connected to pressure, is adapted tobe operated by a synchronizing circuit 14 and allows actuating unit tobe alternately connected to pressure and vented. Thus, only when thevalve 13 is actuated by the synchronizing circuit 14 does the valve 13cut off the supply of compressed gas to the actuating unit 15 which inturn controls the action of the pumping unit 16.

Directing attention now to the actuating unit 15, it may be the typedisclosed in the aforementioned patent but is preferably of the typecomprising a 10W inertial diaphragm separating the unit into an inputcompartment and an output compartment, the pressurized gas from valve 13being admitted into the input compartment and the gas in the outputcompartment being in communication with the pumping unit 16 throughpressure -line 32, a percutaneous connector and pressure line 33. Theactuating unit preferably is provided with an adjustable stop to preventthe diaphragm from providing a volumetric displacement greater than apreselected amount and in any event not greater than about 60 cc. whichis in the range of the average volumetric displacement of the leftventricle of the human heart. Further, the actuating unit should have alow resistance to maintain the load on, the heart as low as possiblesince the heart must move the diaphragm unless the input compartment iscoupled at the appropriate time to an appropriate back pressure throughvalve 13 during diastole.

Mounted or affixed to the actuating unit 15 is ia transducer 27 actuatedby actuating unit 15. This may be accomplished in conventional fashion,for example, by providing a mechanical connection such as a rod betweenthe transducer 27 and the aforementioned diaphragm in the actuating unit15. While the particular type of transducer used is not critical, itshould preferably provide a direct current signal, the magnitude andpolarity of which is representative of the movement of the diaphragm.Thus, if the diaphragm is moving, the output signal of the transducer 27will be a varying but unidirectional signal, if the diaphragm stops inany particular place, the output signal will be a direct currentvoltage, when the diaphragm reaches one end of its travel, the outputsignal will be of a maximum value of given polarity, and when thediaphragm reaches the other end of its travel, the output signal will.again be of a maximum value but of opposite polarity. For a morecomplete discussion of a suitable actuating unit, reference is made topatent application Ser. No. 568,248, filed July 27, 1966 by Michael L.R'ishton `and assigned to the same assignee.

A typical pumping unit comprises a rigid case containing a collapsiblebulb, the outer surface of which is in communication with a pressurizedgas (the output compartment of the pumping unit 15) and the innersurface of which is in communication with the circulatory system of abody. A typical extracorporeal ventricle is disclosed in theaforementioned U.S. Patent No. 3,099,- 260 and a typical intercorporealventricle is disclosed in the aforementioned patent application Ser. No.355,273.

ABy way of example, the rod actuated by the diaphragm may be movableinto and out of a coil to vary the output frequency of an oscillatorwhich is rectied to provide either a constant direct current signal or avarying direct current signal, depending on the movement of thediaphragm.

Since the zero position of a low inertia diaphragm can move or be madeto move because, for example, of a slow leak, changes in pressure,diifusion of the gas through the bulb and/ or tubing and the like, anadjustable centering valve 31 coupling the input compartment and theoutput compartment of the pumping unit is provided for centering and/ orrecentering of the diaphragm. Centering valve 31 may comprise aconventional manually or automatically adjustable valve to provide thedesired flow rate between the input compartment and the outputcompartment when a difference of pressure exists between them. Such anarrangement or its equivalent is essential to insure that a givenvolumetric displacement in the actuating unit 15 is reflected in thepumping unit 16.

Attention is directed to the fact that three-way valve 13 is vented toatmosphere through diastolic back-pressure producing means 30. Means 30may comprise, for example, a volume large with respect to the volumetricdisplacement of actuating unit 15 and ian adjustable needle valve or thelike (not shown) to permit controlled venting of actuating unit 15 andthereby provide a back pressure substantially equal to the diastolicpressure of the patient. The provision of a diastolic back pressure isessential to insure that output signal of transducer 27 isrepresentative of diastole in the patient. It has been found that ifdiastolic back-pressure producing means 30 is not provided, not `onlywill back flow of blood into the pumping unit 16 occur, but duringdiastole the diaphragm now actuated 'by the diastolic pressure in thecirculatory systern ywill be permitted to move at a rate notrepresentative of pressure lin the circulatory system during diastole.This has the added disadvantage of resulting in undue Wear on the bulb'by permitting it to strike the case at the end of its diastolic stroke.

All of the foregoing components with, of course, the exception of thepercutaneous connector and pumping unit may be located in a Ibedsidecontrol panel. Tube 32 connects the pneumatic portion of the system tothe patient in which is implanted the percutaneous connector 25 and thepumping unit 16. Tube 33 which is disposed interior of the body connectsthe percutaneous connector to the pumping unit.

Broadly, the action of both the actuating unit and the pumping unit mustbe capable of being synchronized with the patients heart. The actuatingunit and hence the pumping unit must be capable of being phased with thepatients heart while the duration of the systolic and diastolic strokesshould be adjustable. The synchronizing circuit 14 performs the functionof properly synchronizing the operation of the solenoid in valve 13 foradmitting the pressurized gas into the actuating unit 15 in accordancewith the demands of the patient. Typically, the synchronizing circuit isactuated by the patients electrocardiogram or the R-wave (not shown)taken directly from his heart. By way of example, the output of an -EKGunit may be fed into an amplifier and synchronizer pulse Shaper circuitthat is adapted to amplify the sync pulse or electrical signal used forsynchronizing purposes. The amplifier and synchronizing pulse Shaper maybe designed not only to limit the magnitude of the sync pulse but alsoto shape it. The actuating unit is preferably synchronized with theR-wave portion of the sync pulse and all other portions of the wave mayaccordingly either be reduced or removed, thereby leaving only theR-wave. Since the hydraulic events in the patients heart are notsimultaneous with the EKG unit or the R-wave and, furthermore, since thehydraulic events in the patients circulatory system are delayed behindthe systolic pulse of the heart by varying amounts depending on thedistance of the artery or vein from the left ventricle of the heart, itis desirable to provide means for phasing the systolic or the diastolicpulse of the pumping unit as the case may be with the systolic pulse ofthe heart in order to accommodate these time delays and provide thedesired time delay.

For the system shown in FIGURE 1, in accordance with the presentinvention, a network triggered by the R-wave is provided to create async pulse delayed behind the actuating R-wave and preceding the nextsucceeding R- wave by a controlled amount to enable the diastolic pulseof the pumping unit to controllably correspond with the systolic pulseof the patients heart. By providing means lfor initiating the diastolicpulse of the pumping unit a controllable time interval prior to thebeginning of the hearts systolic pulse (because of time delays inherentin all mechanical systems) and terminating the diastolic pulse of thepumping unit a controllable time interval after it has been initiated,the pumping unit may be satisfactorily phased with the events in thecirculatory system of substantially any patient. Further, the timeconstant of the delay network (exclusive of any manual adjustment) isdependent on the time interval between a plurality of prior R-waves,typically one to about five. Accordingly, even though a patients heartbeat may vary from its normal rate to, for example, a higher rate, thetime at which the diastolic pulse of the pumping unit is initiated will,except for arrhythmia and/ or high rates of change, occur atsubstantially the same time interval prior to the next succeedingR-wave.

Directing attention now to FIGURE 2, which shows details of thesynchronizing circuit 14 of FIGURE 1, the output of an EKG unit, orpreferably the R-wave taken directly from the patients heart (not shown)comprising a synchronizing signal is fed to an amplifier and pulseshaper circuit 40 of conventional design to provide an output signalrepresentative of the R-wave. Accordingly, the amplifier and pulseShaper circuit 40 may in conventional manner limit the amplitude of thesynchronizing signal and reduce or remove all portions of this signalother than the R-wave whereby only that portion of the signalrepresentative of the R-waves is supplied to a conventional blockingoscillator 41. The output of oscillator 41 are sharp narrow pulses of apredetermined and constant magnitude which coincides with the R-Waves ofthe synchronizing signal.

The output of the blocking oscillator 41 is fed simultaneously toalinear sawtooth generator 42 and a storage capacitor circuit 43described in greater detail hereinafter. The output of the linearcharging circuit 41 is a linear ramp or saw tooth wave and the output ofthe storage capacitor circuit 43 is a wave having a short rise time andsmall drop-off after reaching its maximum amplitude. The storagecapacitor circuit 43 is charged by the linear saw tooth generator 42 andthe output of blocking oscillator 41 functions to at least substantiallydischarge the linear saw tooth generator circuit 42 and partiallydischarge the storage capacitor circuit 43 whereby both circuits areactuated simultaneously upon arrival of an R-wave and the amplitude oftheir output signals is proportional to the frequency of the incomingR-waves.

The output signals of the aforementioned circuits are fed to acomparator 44 which may include an amplifier to provide a sharp narrowpulse when the amplitude of the output signals of the two circuits areequal. The amplitude of the output signal from the linear saw toothgenerator circuit 42 or alternately, the output signal of the storagecapacitor circuit 43 may be continuously varied to permit actuation ofcomparator 44 at some preselected time interval prior to the nextsucceeding R-wave. Assuming that the R-wave frequency remains fixed, theamplitude and Wave form of the storage capacitor circuit, for example,remains fixed and is triggered as is the linear saw tooth generatorcircuit by each R-wave as described hereinabove. Accordingly, manualvariation of the amplitude of, for example, the output of the linear sawtooth generator circuit will result in triggering of the comparator fromsubstantially any time shortly after arrival of a triggering R-wave tothe arrival of the next succeeding R-wave. The output signal of thecomparator 44 is fed to a first or advance variable length one shotmultivibrator 45 which is stable in one direction and is tripped intoits other mode of operation by the output signal of the comparator.While the output signal of the comparator can theoretically be useddirectly to determine the advance necessary to initiate action ofthree-way valve 13 (see FIGURE 1), use of the advance multivibrator 45to establish the amount of advance is preferred because of, among otherthings, the sensitivity required of the advance adjustment. Further, asmore fully described hereinbelow, the advance multivibrator 45 permitsan advance as well as a delay, with respect to a succeeding Rewave, ofinitiating action of three-Way valve 13.

Assuming that the comparator 44 is actuated suiciently in advance of thenext succeeding R-wave, as has been found to be easily attainable,multivibrator 45 may be provided with a variable RC circuit to permitadjustment of the time it remains in its tripped condition. Thus,differentation of the output pulse of multivibrator 45 will provide twopips the first of which corresponds with the leading edge of thedifferentiated output pulse and the second of which corresponds with thetrailing edge of the differentiated output pulse and which is fed to asecond or duration multivibrator 46. The duration multivibrator 46 issubstantially identical to the advance" multivibrator 45 and is trippedby the termination of the output pulse of the advance multivibrator 45.The duration multivibrator 46 may also be provided With -a variable RCcircuit to permit adjustment of the time that the three-way valve 13 isactuated which is to say vented and thereby determine the diastolicpulse of the pumping unit 16'. The output of the duration multivibrator46 is fed to a conventional switching circuit 47 comprising the solenoid48 of the three-way valve 13. Thus, when switching circuit 47 isactuated, the circuit supplying current to the solenoid 48 of thethree-way valve 13 is broken and the actuating unit 15 is vented.

Attention is now directed to FIGURE 3 which shows details of theblocking oscillator, saw tooth generator circuit, storage capacitorcircuit and the comparator discussed in connection with FIGURE 2. Asshown in FIG- URE 3, the output signal from the amplifier and pulseShaper 40 is coupled to blocking oscillator 41 comprising transistor 55,capacitor 61, resistor 62 and feed back transformer 63. The emitterelectrode of transistor 55 is connected to ground, resistor 62 isconnected between the emitter and base electrode of transistor 55, andthe primary winding of transformer 63 is connected between B+ and thecollector electrode whereby a portion of the output signal at thecollector electrode is coupled back to the base electrode inconventional manner. The

v input signal to transistor 55 may be of the order of three or fourvolts and the output signal of transistor 55 (which is a sharp negativegoing signal for the embodiment shown) is used primarily to dischargethe ramp capacitor 64 forming part of the saw tooth generator circuit42. The output signal from transistor 55 is taken at its collectorelectrode and coupled to the base electrode of transistor 56 through adiode 65. The collector electrode 0f transistor 56 is connected toground, the emitter electrode being connected to B-lthrough a resistor66 and to the base electrode through resistor 67. Capacitor 64 isconnected between the base and collector electrodes of transistor 56.Transistor 56 and its associated resistors comprise a boot-strap circuitthe function of which is to cause capacitor 64 to charge linearlythrough transistor 56 in the absence of an output signal from transistor55. Accordingly, when an R-wave (or an electric signal derivedtherefrom) is coupled to transistor 55, it fires and its youtput signalcoupled through diode 65 very quickly substantially completelydischarges the capacitor 64. After the output signal from transistor Sdisappears, capacitor 64 begins to again charge up linearly throughtransistor 56 and its emitter resistors until it is discharged by thenext pulse from transistor 55. The function of diode 65 is to couple theoutput signal from transistor 55 to capacitor 64 and in the interimprevent capacitor 64 from discharging into the collector electrode oftransistor 55. It should be noted at this point that the plate side ofdiode 65 is connected to B-lwhereas the cathode side is connected tocapacitor 64. Accordingly, capacitor 64 continually tries to chargelinearly to B+, but when the negative output signal from transistor 55is coupled to capacitor 64, the voltage on capacitor 64 drops rapidly toessentially zero. Thus, as will now be seen, in the boot-strap circuitdisclosed hereinabove, capacitor 64 is linearly charged throughtransistor 55 and is very rapidly discharged through diode 65 to providea linear saw tooth voltage the frequency of which corresponds to thefrequency of the R-Waves coupled to transistor 5S. The aforementionedlinear saw tooth voltage appears across emitter resistor 66 and iscoupled directly to the base electrode of transistor 57 which comprisesan emitter follower. Transistor 57 functions in conventional manner toprovide a high input impedance to prevent distortion of the signal atthe emitter electrode of transistor 56 and a very low output impedanceat its emitter electrode. The linear saw tooth voltage appearing at theemitter resistor 66- is coupled through transistor 57 and appears acrossemitter resistors 71 and 72 connected between the emitter electrode oftransistor 57 and ground. Resistor 71 is provided with an adjustable tapto permit a portion of the linear saw tooth voltage appearing at theemitter electrode of transistor 57 to be coupled to the base electrodeof transistor 60 as and for the purposes hereinafter described. Theoutput signal of transistor 57 is taken from its emitter electrode andis coupled through diode 73 to capacitor 74 and the base electrode oftransistor 58, Diode 73 is poled to prevent capacitor 74, which yispreferably a storage capacitor, from discharging through resistors 71and 72 which may have a total resistance of about five thousand ohms.Diode 76 and resistor 77, which are connected between the collectorelectrode of transistor 55 and capacitor 74, function to partiallydischarge capacitor 74 when an output signal appears at the collectorelectrode of transistor 55. Resistor 77 preferably is adjusted or chosenwhereby when an output signal appears at the collector electrode oftransistor 55, only a small portion such as, for example, ten to fifteenpercent of the charge stored in capacitor 74 will be discharged throughthis portion of the storage capacitor circuit. The storage capacitorcircuit 43 comprises capacitor 74, diode 76 and resistor 77. Capacitor74 is charged by the saw tooth output voltage of transistor 57 and ispartially discharged through substantially only resistor 77 and diode76. The voltage across capacitor 74 varies essentially exponentiallywithin relatively small limits and is coupled through transistor 58 totransistor 59. Transistor 58 together with resistors 75 and 78 comprisesan emitter follower which functions to provide a high input impedance (ahigh impedance across capacitor 74 as resistor 75 is selected to have ahigh resistance) and a low output impedance (a low i-mpedance at itsemitter electrode) for driving transistors 59 and 60 which comprise thecomparator circuit 44.

As will now be apparent, for a given R-wave frequency, the voltageacross capacitor 64 will be a saw tooth that varies linearly from zeroto some plus value and the voltage across capacitor 74 will varyexponentially. Whereas the amplitude of the voltage across capacitor 64increases linearly from zero after receipt of an R-wave, the voltageacross capacitor 74 will simultaneously rise Very quickly from somevalue slightly less than its maximum value and thereafter drop ofi veryslowly, the maximum amplitude of both voltages being essentiallydetermined by the time interval between one or more preceding R-waves.Further, Whereas the charge on capacitor 64 is essentially completelydissipated upon receipt of each R-wave, the charge on capacitor 74 isonly partially removed.

For the embodiment shown in FIGURE 3, transistors 59 and 60 comprise acomparator circuit. Transistors 59 and 60 are connected in conventionalmanner as shown to form a well known comparator circuit with theexception that transistor 59 is connected to provide an output impedanceat its emitter electrode that is even lower than the output impedance atthe emitter electrode of transistor 58. As compared to the amplitude ofthe linear saw tooth voltage at the emitter of transistor 57, theamplitude of the signal at the emitter electrode of transistor 59 isreduced. By way of example, one may expect a voltage drop of about 0.6volt across respectively diode 73, transistor 58 and transistor 59.

Accordingly, at the emitter electrode of transistor 60, the voltage atthis point may Ibe expected to be -approximately one and one-half to twovolts less than that at the emitter electrode of transistor S7. As willnow be apparent, the amplitude of the voltage coupled from the emitterelectrode of transistor 59 through resistor 79 to the emitter electrodeof transistor 60 is essentially equal to the peak value of the saw-tooth voltage at the emitter electrode of transistor 57 minusapproximately one and one-half volts. The saw tooth voltage is coupledto the base electrode of transistor 60 from resistor 71 in the emittercircuit of transistor S7. It is necessary that the amplitude of thelinear ramp voltage supplied to the base electrode of transistor 60 bemade adjustable so that the amplitude of the saw tooth voltage and thestorage capacitor voltage will coincide at some predetermined andselectable time prior to the arrival of the next succeeding R-wave, andprovide an output pulse at the collector electrode of transistor 60.

The output signal of transistor 60 is a signal which rises rather slowlyand for this reason may be coupled to one or more amplifiers (not shown)prior to coupling 1t to the advance multivibrator 45 to provide a fastrising signal having an amplitude of, for example, five to six volts. Asdiscussed in connection with FIGURE 2, this signal is used to triggerthe variable length advance multivibrator 45 which essentiallydetermines when the actuating unit will be vented to atmosphere.

The provision of a saw tooth generator circuit and a storage capacitorcircuit as described hereinabove is particularly advantageous in that itpermits the comparator circuit to be triggered sufficiently in advanceof the next succeeding R-wave to permit the provision of advancemultivibrator 45, the pulse length of which can be Selected to provideeither an advance or delay, as compared to the next expected R-Wave ofthe systolic pulse of the actuating unit. As previously described,multivibrator 46 determines the length of the systolic pulse of theactuating unit. Further, because of the partial discharge of capacitor74, even in the presence 0f a rapid change in frequency of the patientsR-Wave, the described circuits automatically provide advance actuationof the actuating unit at the preset time interval within a matter ofonly a few heart beats.

The various features and advantages of the invention are thought to beclear from the foregoing description. Various other features andadvantages not specifically enumerated will undoubtedly occur to thoseversed in the art, as likewise will many variations and modifications ofthe preferred embodiment illustrated, all of which may be achievedwithout departing from the spirit and scope of the invention as definedby the following claims.

What is claimed is:

1. In a circulatory assist system including means for producing anelectric signal that is a direct function of the pumping action of thepatients heart, an actuating unit and a blood pumping unit controlled bysaid actuating unit, the combination comprising:

(a) first and second charging circuit means, said second chargingcircuit means being charged through said first charging circuit meansand attains and substantially retains its maximum charge substantiallyprior to that of said first charging circuit means;

(b) means for coupling said electrical signal to said first and secondcharging circuit means; and

(c) means for controlling the operation of said actuating means inresponse to the output signals of said first and second charging circuitmeans for phasing the systolic pulse of said actuating unit with thediastolic pulse of the patients heart.

2. The combination as defined in claim 1 wherein said first chargingcircuit means comprises a linear saw tooth generator and said secondcharging circuit means includes a storage capacitor circuit.

3. The combination as defined in claim 2 wherein said means for couplingsaid electrical signal to said first and second charging circuits meansincludes first means for substantially completely discharging said firstcharging circuit means and second means for only partially dischargingsaid second charging circuit means when said first charging circuitmeans is discharged.

4. In a synchronizing circuit in a circulatory assist system forsynchronizing the pumping action of an actuating unit which controls theaction of a blood pumping unit with the pumping action of the patientsheart wherein said synchronizing circuit is responsive to the patientsR-Wave, the combination comprising:

(a) means for providing an electric signal that is a direct function ofthe patients R-wave;

(b) a first charging circuit for providing a linear saw tooth outputsignal;

(c) a second charging circuit coupled to the output of and charged bysaid first charging circuit;

(d) first means for coupling said electric signal to said first andsecond charging circuits whereby said first and second charging circuits-are simultaneously discharged in synchronism with the patients R-wave,said first circuit being substantially discharged but said secondcircuit being only partially discharged; and

(e) second means for controlling the operation of said actuating meansin response to the output sign-als of said first and second chargingcircuit means for phasing the systolic pulse of said actuating unit withthe diastolic pulse of the patients heart.

'5. The combination as defined in claim 4 wherein the time constant ofsaid second charging circuit is short compared to that of said firstcharging circuit and additionally including third means for varying theamplitude of the output signal of one of said charging circuits wherebythe amplitude of said saw tooth signal equals the amplitude of theoutput signal of said second charging circuit prior to the nextsucceeding R-Wave.

6. The combination as defined in claim 5 wherein said second chargingcircuit includes a storage capacitor coupled to the output of said firstcharging circui-t and said first means includes a diode and resistorcoupled between said stora-ge capacitor and the output of said means forproviding said electric signal.

7. The combination as defined in claim 5 wherein Said second meansincludes:

(a) comparator circuit means for providing an output signal when theamplitude of the output sign-als of said first and second chargingcircuits are equal;

(b) a first one-shot multivibrator triggered by the output of saidcomparator circuit means, said first multivibrator including means forcontrolling the time it remains in its -triggered condition; and

(c) a second one-shot multivibrator triggered fby the output of saidfirst multivibrator, said second multivibrator including means forcontrolling the time it remains in its triggered condition.

8. The combination as defined in claim 7 wherein said second meansadditionally includes a solenoid that is responsive to the output signalof said second multivibrator to control a valve, said valve directing anoperating medium into said actuating unit for causing the operationthereof.

References Cited UNITED STATES PATENTS 3,099,260 7/1963 Birtwell 128-13,266,487 8/ 1966 Watkins et al 128-1 DALTON L. TRULUCK, PrimaryExaminer.

U.S. Cl. X.R. 12S-214

